How good is it, how well do the characters seem to fit in?
It's a pretty good series so far. I'd give the first issue 3.5/5. The characters don't really fit in but I think that's kind of the point. I'll be more interested once the book actually gets the team together, because the first issue was mostly just a lot of exhibition on the characters. So far, my favorite character appearances have been Green Arrow, Hawkman, and Martian Manhunter.
I finally read it (saw this thread but had to stay away until I had) and I'm really looking forward to it developing. I REALLY love this new Martian Manhunter so far (I saw a little of him on Stormwatch, but the rest of the book didn't interest me so I dropped it). He seems much more confident & not afraid to throw his weight around than pre-52 Jonn (I really don't think I've said that yet, liking a new-52 character better than their pre-52 version). I had previously thought the MM-backup started right away, so I was a little disappointed there, but can't wait to read it next time. (If it wasn't clear, he's the main reason I'm very excited for this title, haha. If you subtracted him from the team, I probably would cae MUCH less). I can't wait to find out all the unspoken "reasons" dropped throughout the issue.